Poor hoist spooling can be characterized by the presence of gaps between cable wraps, multiple cable layers on a drum designed for single-layer cable wrapping, mechanical cable damage, reduced productivity, reduced cable life, and/or operator injury. Mechanical damage to a cable can be caused by “bird-caging” and formation of loops and/or kinks.
These problems often arise when a hoist spooling assembly is used to lift or lower a drill string. As a drill string is lowered into a drill hole, its velocity will sometimes decelerate relative to the constant velocity of the cable line of the main line hoist. This deceleration can be attributed to an obstruction or to the viscous effects of drilling mud or water in the drill hole. This change in relative velocities can result in an excess amount of cable, which, in turn, can lead to formation of a loop. If such a loop is pulled through the hoist spooling assembly, a kink can form, thereby damaging the cable such that the cable is unfit for service. Kinks of this kind often form when the hoist operator stops activating the winch and the drill string breaks free of the obstruction, thereby allowing the full weight of the drill string to be applied to the cable with loops present. If the loops are large enough, then they can also get caught on—and irreparably damage—any tensioning mechanisms or encoders of the assembly. Slack in the cable can also arise when there are gaps between cable wraps. When these gaps occur, the length of the cable in a single wrap is longer than the length of the cable in a properly spooled wrap. Thus, when the cable shifts laterally on the drum, the extra length creates slack that can cause damage as described herein.
When a hoist is used to lift the drill string, a hoist plug must typically be threaded on the drill rods. Often, the hoist plug is lowered into the drill string with an excessive amount of unwound cable having little or no tension. Subsequent activation of the hoist can cause a sudden application of tension force to the cable, which is typically at a fleet angle of 1 to 2 degrees relative to a center of the drum. This sudden application of force can result in a side load that forces the cable to “jump” towards the center of the drum, thereby creating a gap. Over time, these spooling errors can perpetuate until the rope is damaged or until the operators are required to re-spool the rope, which can result in severe operator injury.
Accordingly, there is a need in the pertinent art for apparatus and methods for preventing relative motion between a cable and a drum, optimizing the interface between a roller and the cable, and improving the overall functionality and robustness of a hoist spooling assembly in drilling applications.